Efforts are under way to free a nuclear-powered submarine which ran aground in shallow waters.
HMS Astute was on sea trials when the rudder of the vessel is thought to have become stuck on a shingle bank between the mainland and the Isle of Skye on the west coast of Scotland at around 8am on Friday.
There were no reports of any injuries and the Ministry of Defence insisted it was not a "nuclear incident".
The coastguard was at the scene and an earlier attempt to tow the submarine failed, according to eye witnesses. Royal Navy vessels and a tug will help free the submarine at high tide later on Friday.
It is believed a crew transfer from the shore to the submarine was being carried out when the incident happened. The rudder will be inspected once the vessel is freed.
Eyewitness Rachel Browett, who runs the Bright Water Visitor Centre on Skye, said: "It's not too far from the shore and clearly visible from the bridge. I could see steam or smoke coming from the top and about half the sub was visible. A few boats were around about it in the water and a helicopter went overhead at one point, though I don't know if it was involved."
Meanwhile, the commanding officer of HMS Astute could find himself in front of a court martial as a result of the grounding.
Royal Navy experts have launched a detailed investigation, known as a service inquiry, into why the embarrassing incident occurred. Military prosecutors will then consider whether HMS Astute's skipper, Commander Andy Coles, or any of his crew was negligent.
A defence source said it was likely that Cdr Coles, as the officer in ultimate charge of the advanced nuclear-powered submarine, would face a court martial. Members of HMS Astute's crew could be charged with performing a duty negligently or "hazarding" one of Her Majesty's ships through negligence.